Method of cleaning work objects having limited temperature tolerance



United States Patent METHOD OF CLEANING WORK OBJECTS HAVING LIMITED TEMPERATURE TOLERANCE Thomas J. Kearney, Detroit, Mich., assignor to Detrex Corporation, Detroit, Mich., a corporation of Michigan No Drawing. Application September 24, 1953,

' Serial No. 382,205

4 Claims. (Cl. 134--11) This invention relates to a method of cleaning work objects in methylene chloride vapor or clean boiling solution, and more specifically relates to a method of cleaning or degreasing and concurrently checking thermometers.

Thermometers such as glass clinical thermometers are conventionally calibrated by etching. In carrying out the etching step, the thermometers are coated with wax, marked and the marked portions etched, usually in hydrofluoric acid. After etching has been accomplished and the parts have been thoroughly rinsed, the wax is removed. Inasmuch as the thermometer can usually be subjected to a maximum temperature of only about 110 F., or of the order of 105 -115 F., without damaging its calibration or actually destroying its further use as a thermometer, there is a need for a safe and non-inflammable as well as an economical means and method of removing wax and the like.

It is important to remove the wax in such a manner that the dewaxed thermometers are clean and dry, as the next step in the manufacture of the thermometers is to press into the etched markings a colored material which renders the calibrations more readily visible.

One of the present methods used for dewaxing thermometers includes the step of immersing the thermometers for about four to five hours in a selected hydrocarbon solvent at room temperature, after which each thermometer must be individually hand wiped to remove the residual solvent. This operation is slow, laborious, and presents a fire hazard. Moreover, the thermometers must be brought to a preselected temperature and the calibrations of each thermometer individually checked for accuracy.

It is accordingly an object of this invention to provide a safe, economical, rapid method of cleaning work objects. A more specific object of the invention is to clean work objects which are subject to damage at temperatures above the normal maximum atmospheric temperatures.

Still another object of this invention is to provide a simple and rapid method of cleaning and concurrently checking a thermometer having a scale including temperatures in substantially the range 100-105 F., more specifically, 103l04 F.

Other objects and advantages of the invention, including the simplicity and economy of the same, will further appear in more particular detail hereinafter.

In accordance with this invention methylene chloride vapor is formed, the temperature of the vapor being substantially equal to the boiling point of methylene chloride, or 103.6 F. The objects to be cleaned are disposed in the clean boiling liquid or vapor and are maintained in the liquid or vapor for a time sufiicient to complete the cleaning operation. Upon removing the articles from the methylene chloride they are clean and dry.

The cleaning step may readily be carried into effect in a degreaser wherein methylene chloride liquid is heated and distilled in a tank and the resulting vapors are conand spray type degreasing, utilizing a combined vapor,

spray apparatus such as the degreasing machine shown and described in my copending patent application entitled Decreasing Apparatus, Serial No. 290,249, filed May 27, 1952, Patent No. 2,700,645, dated January 25, 1955.

Accordingly, work objects may be contacted by substantially pure methylene chloride vapor or liquid or by methylene chloride vapor and spray combined. In neither case does the temperature of the cleaning material substantially exceed the boiling point of methylene chloride, namely 103.6 F.

In the cleaning of clinical or other thermometers which are subject to breakage or other damage at temperatures; above about -115 F., methylene chloride vapors heat the thermometers up to the temperature of the vapors, namely, about l03.6 F., but no higher. This fact not only guards the thermometers against damage but affords a ready means for checking the accuracy of the thermometer calibrations. The method is particularly advantageous for cleaning and checking thermometers of the maximum reading type, since batches of cleaned thermometers may be allowed to cool to room temperature, which is only slightly below the temperature of the degreasing vapor, for ultimate checking at any convenient time. It is also desirable to place a thermometer, known to be accurate, in the vapor zone of the degreaser, such thermometer indicating accurately the maximum temperature to which the other thermometers had been subjected. However, the boiling point of substantially pure methylene chloride of itself gives an accurate check.

It will be appreciated that, although this invention is particularly advantageous inconnection with the combined cleaning and checking of thermometers, it has a wide variety of advantageous uses. For example, in the vapor-spray type of degreasing equipment, it is possible by means of the solvent vapors augmented by a spray of solvent distillate to clean assembled devices such as transmission housings, gas meters and other similar devices which are already packed with lubricant and should not be subjected to temperatures in excess of maximum atmospheric temperatures. However, it is often necessary that the oil and grease accumulating on their exterior during assembly be thoroughly removed prior to painting. No method known to me, other than the method of this invention utilizing methylene chloride in the liquid and vapor phase, will clean these parts and at the same time allow them to be removed from the process clean and dry, rapidly, and still never subjecting them to temperatures in excess of 103.6 F. This temperature is often encountered in various parts of the United States and is not believed to be in excess of temperatures to which the items might normally be subjected in ultimate use.

Methylene chloride has particular solvent properties making it highly advantageous. For example, it is superior to trichlorethylene and perchlorethylene in the removal of polyethylene, polyester and styrene polyester which are often used to impregnate aluminum and magnesium castings.

Methylene chloride degreasing in according with this invention is also highly advantageous for degreasing precision metal articles where precision gauging is required immediately after complete degreasing. Prompt gauging is often required from a production requirement standpoint or where gauging must be done promptly after cleaning prior to rust proofing. In accordance with this invention, a minimum time interval can be allowed between the time the part leaves the degreasing cycle and the time it is recoated with a rust preventative, such as accelerated dihydrogen phosphate coating chemicals, for example.

Despite its low vapor density, which is 2.94 as compared to trichlorethylene at 4.53 and perchlorethylene at 5.72, the diffusion of methylene chloride from a degreasing machine into air does not appear to exceed the diffusion of trichlorethylene and perchlorethylene. This apparently is accounted for by virtue of the smaller temperature difference between the methylene chloride vapors and the air. Thus the velocity imparted to the solvent vapors due to convection is held to a minimum. It is found that the solvent loss and diffusion therefore is not necessarily proportional to the vapor density and that practical and economical solvent consumption is accomplished in accordance with this invention.

While I have disclosed the invention with reference to certain specific embodiments adapted for specific purposes, it will be appreciated that the method may be modified by the substitution of equivalents, that certain of the steps may be reversed, and that certain features may be utilized independently of the use of other features, all within the spirit and scope of the invention as defined in the appended claims.

Having thus described my invention, I claim:

1. In a method of cleaning an article which has an oily or greasy surface and which consists essentially of a solid material which is insoluble in methylene chloride and which is damaged when heated to about 105-115 F., the steps which comprise boiling methylene chloride liquid solvent forming a substantially pure methylene chloride vapor above said liquid, said vapor being at substantially atmospheric pressure and being substantially free of organic impurities and having a temperature substantially equal to the boiling point of pure methylene chloride at atmospheric pressure, which is about 103.6 F., condensing the solvent vapors, collecting the resulting liquid methylene chloride distillate, contacting the article with the methylene chloride vapor and with liquid methylene chloride distillate to degrease the same, and removing the article from the methylene chloride.

2. In a method of cleaning and concurrently checking a maximum reading thermometer which has capacity to measure and indicate temperatures of about 103 and 104 F., the steps comprising forming a methylene chloride vapor zone in equilibrium with substantially pure boiling methylene chloride at about atmospheric pressure, inserting the thermometer into said vapor for a time sumcient to attain a maximum reading, and removing the thermometer from the vapor whereby the thermometer is degreased and whereby its accuracy may be checked by comparing the maximum thermometer reading with the boiling point of said methylene chloride.

3. in a method of cleaning a thermometer having a maximum reading of the order of about 105115 F., said thermometer being subject to damage at temperatures in excess of about F., the steps which comprise forming a vapor zone consisting of methylene chloride vapor at a temperature of about 103-l04 F., disposing the thermometer in the methylene chloride vapor to clean the thermometer, and removing the thermometer from the vapor.

4. In a method of dewaxing a glass thermometer which has been marked by forming etchings on portions of the glass while protecting other portions of the glass from the etching medium by the application of a wax coating, the steps which comprise continuously boiling vapors from the surface of substantially pure liquid methylene chlo ride at a temperature of about 103104 F., continuously condensing methylene chloride vapors at a location spaced above the methylene chloride liquid surface thereby forming a methylene chloride vapor zone above the liquid, said vapor zone having a temperature of about 103104 E, placing the waxed and etched glass thermometer in the vapor zone for a time sufficient to remove the wax, and removing the thermometer from the vapor.

References Cited in the file of this patent UNITED STATES PATENTS Dinley Dec. 14, 1937 KBurg Feb. 13, 1951 OTHER REFERENCES 

1. IN A METHOD OF CLEANING AN ARTICLE WHICH HAS AN OILY OR GREASY SURFACE AND WHICH CONSISTS ESSENTIALLY OF A SOLID MATERIAL WHICH IS INSOLUBLE IN METHYLENE CHLORIDE AND WHICH IS DAMAGED WHEN HEATED TO ABOUT 105-115* F., THE STEPS WHICH COMPRISES BOILING METHYLENE CHLORIDE LIQUID SOLVENT FORMING A SUBSTANTIALLY PURE METHYLENE CHLORIDE VAPOR ABOVE SAID LIQUID, SAID VAPOR BEING AT SUBSTANTIALLY ATMOSPHERIC PRESSURE AND BEING SUBSTANTIALLY FREE OF ORGANIC IMPURITIES AND HAVING A TEMPERATURE SUBSTANTIALLY EQUAL TO THE BOILING POINT OF PURE METHYLENE CHLORIDE AT ATMOSPHERIC PRESSURE, WHICH IS ABOUT 103.6* F., CONDENSING THE SOLVENT VAPORS, COLLECTING THE RESULTING LIQUID METHYLENE CHLORIDE DISTILLATE, CONTACTING THE ARTICLE WITH THE METHYLENE CHLORIDE VAPOR AND WITH LIQUID METHYLENE CHLORIDE DISTILLATE TO DEGREASE THE SAME, AND REMOVING THE ARTICLE FROM THE METHYLENE CHLORIDE. 